This invention relates to boiler.
Boilers comprising a heat exchanger and a gas or oil burner assembly for heating a fluid, usually water, circulated through the heat exchanger are well known.
Such boilers are commonly used in hot water and central heating systems where the heat exchanger is connected in a circuit passing through a storage cylinder for the hot water supply and the desired number of space heating devices.
With the increase in cost of gas and oil, considerable attention has been directed to improving the efficiency of such boilers to reduce running costs. For example, it is known to improve efficiency by increasing the surface area of the heat exchanger available for heat transfer and/or to construct the heat exchanger from materials having high thermal conductivities.
Neither of these methods however solves the problems caused by the formation of a boundary layer of cooler slower moving combustion products at the heat exchange surface or of a film of condensed moisture on the heat exchange surface both of which have an insulating effect and reduce the efficiency.
Furthermore, both methods increase manufacturing costs while many of the high thermal conductivity materials are susceptible to attack by the moisture and hot acidic gases contained in the combustion products causing a build-up of corrosion deposits on the heat exchange surface which reduce efficiency and result in eventual failure of the heat exchanger.
It is an object of the present invention to provide a boiler which mitigates at least some of the drawbacks afore-mentioned.